Browsing by Person "Schumacher, Stefan"

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Grapevine Pinot gris virus spreads in infected vineyards: latent infections have no direct impact on grape production
(2024) Messmer, Noemi; Bohnert, Patricia; Askani, Lars; Schumacher, Stefan; Voegele, Ralf T.; Fuchs, René
Background: Grapevine Pinot gris virus (GPGV) infects grapevines worldwide and causes symptoms such as chlorotic mottling and deformations on leaves, stunted shoots and short panicles, or none of these symptoms if it appears as latent infection. So far, the consequences of GPGV infections for winegrowers are difficult to assess since important information such as plant performance at different GPGV infection levels and symptom expression are not fully clarified. Methods: In order to investigate the course of GPGV spread, annual visual evaluations and ELISA tests were conducted over 3–4 consecutive years in four GPGV-infected vineyards in southern Germany: GEM, HEC, NIM, and REI. The program PATCHY was used to analyze spatial disease patterns. Sanger sequencing was used to determine virus isolates in vines at different GPGV infection levels, to test their respective influence on symptom expression. Yield and GrapeScan (FTIR) analyses were conducted to test the impact of different GPGV infection levels and isolates on fruit quantity and quality. Results: GPGV infections significantly increased in all four vineyards (GEM 22–32%, HEC 50–99%, NIM 83–90%, REI 56–76%) with significant spreading patterns across and along rows. Specific symptom progression patterns were not observed. According to our results, the virus isolate has an influence on whether symptoms develop during a GPGV infection. While yield analyses revealed that yield losses only occur in symptomatic vines and range from 13 to 96% depending on the severity of symptoms, latent infections have no impact on grape production. No relevant effects of GPGV infections on must quality were observed. Conclusions: Secondary spread of GPGV was observed in all vineyards monitored, indicating vector-borne transmission that is likely to be accelerated by human viticultural management. GPGV should be further monitored to prevent the accumulation of detrimental symptomatic isolates. The results of this study can be used to assess the risk of GPGV to viticulture and should be considered when developing management strategies against the virus.
Molekulare und biochemische Charakterisierung von NEP1 - ähnlichen Proteinen (NLPs) aus Plasmopara viticola
(2017) Schumacher, Stefan; Vögele, Ralf
Plasmopara viticola, the causal agent of grapevine downy mildew is one of the most important diseases in viticulture and leads to significant losses in crop in years with beneficial weather conditions. The molecular processes during the interaction between this pathogen and vine are yet poorly understood. Adopted pathogens achieve an infection by avoidance or suppression of plant innate immunity. This suppression takes place through pathogen secreted effector molecules, which can modulate plant defense mechanisms in all kinds of ways. One of these effector families are the necrosis and ethylene inducing peptide 1 – like proteins (NLP). These proteins occur in a vast variety of microorganisms and can on the one hand act as virulence factors and on the other hand induce a broad spectrum of defense responses in plants. In necrotrophic or hemibiotrophic pathogens these proteins are formed when the organism starts to feed from dead plant material. Beside these cytotoxic proteins many non-cytotoxic NLPs are known from hemibiotrophic or biotrophic microorganisms. However, the particular function of these NLPs is so far unknown. To date NLPs from Hyaloperonospora arabidopsidis, causal agent of downy mildew on the model plant Arabidopsis thaliana, are the only known example for these proteins from an obligate biotroph plant pathogen. These NLPs are not able to induce necrosis and their roll during infection by the pathogen is so far unknown. During this work two NLPs of complete size as well as one truncated version were identified in the genome of the obligate biotrophic oomycete Plasmopara viticola. During further experiments these proteins had been characterized by the use of molecular biological and biochemical techniques. The studies revealed a high degree of conservation of the corresponding genes isolated from several resistant and susceptible grapevine cultivars. Gene expression analysis showed high PvNLP expression during early time points of infection and even before first contact with host plant material, respectively. Necrosis-inducing activity of PvNLPs was neither observed in the model plant Nicotiana benthamiana nor in different susceptible and resistant Vitis species. To further investigate the reasons for the non-cytotoxic character of these proteins several experiments were conducted to clarify the relevance of different structural regions, their affinity to form homo- and hetero oligomers, as well as their subcellular localization. The crucial component for the lack of cytotoxicity was not identified. Neither the presence of a signal peptide nor a Nterminal region from another NLP with cytotoxic characteristics were able to form a necrosis inducing fusion protein with one of the identified NLPs from P. viticola. Formation of homodimers was observed for PvNLPs in vitro, but apparently does not occur during expression in planta. Furthermore PvNLPs are localized in the cytoplasm of N. benthamiana cells and show a possible association with the plant cell nucleus. This pattern of subcellular localization was also observed for a NLP with necrosis-inducing activity. The ability to induce plant innate immunity in Vitis could not be attested, suggesting a possible lack of the corresponding receptor in this plant genus. The results of this work further suggest a different role of non-cytotoxic NLPs which in P. viticola may fulfill a function during early infection stages ranging from zoospore release until the successful penetration of the host plant Vitis vinifera.